Abstract:

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Internal friction of Ti-24mol%Nb-3mol%Al (Ti-24Nb-3Al) shape memory alloy with a
well-developed texture was investigated by dynamic mechanical analysis (DMA) in a tensile mode
with a frequency of 1Hz and a temperature range of 123~423K. Ti-24Nb-3Al alloy fabricated by
Ar arc-melting was cold-rolled with a reduction in thickness of 99% and then heat-treated at 1173K
for 3.6ks in vacuum to develop a recrystallization texture. The martensitic transformation
temperature and internal friction (tan δ) were evaluated under the stress amplitude of 36MPa. The
tensile direction was selected to be the rolling direction (RD) and the transverse direction (TD).
The specimen was β-single phase with a well-developed {112}β<110>β texture at room temperature
and exhibited high damping during martensitic transformation and in the martensite phase. The
relationship between internal friction and the tensile direction is discussed on the view point of the
crystallography of the transformation.

Abstract: The stir-casting method was utilized in this paper to synthesize 6063Al/Al2O3·SiO2
reinforced composites consisting of 6063Al alloy as matrix and Al2O3·SiO2 particles as additive with
content of 5%, 10%, 15%, 20% (volume fraction) respectively. Al2O3·SiO2 particles were obtained
from fly ash particles of Steam Power Plant and were pretreated. The shape of these fly ash particles
was spheroidal and ellipsoidal. The damping behavior of 6063Al/Al2O3·SiO2 particle reinforced
composites was studied by measuring the composite’s internal friction values on a Multifunctional
Damping Measurement Apparatus. Under the condition of this series of experiments,
6063Al/Al2O3·SiO2 particle reinforced composites had a higher internal friction values than that of
6063Al matrix and also showed the dependency of internal friction on Al2O3·SiO2 particles volume
fraction, particles dimension, vibration frequency and temperature. There was an increased trend for
internal friction values with increasing the volume fraction of Al2O3·SiO2 particles and decreasing
particles dimension of Al2O3·SiO2 at the same frequency and the different temperature. It has been
found that in the lower frequency, the higher internal friction value was obtained. The internal friction
of the composites increased with increasing temperature. In the case of lower frequency, two damping
peak were observed. A low-temperature damping peak appeared at a temperature near 245°C which a
high-temperature damping peak appeared near 450°C. Based on the experimental results, the
damping mechanism of 6063Al/Al2O3·SiO2 particle reinforced composites was preliminary
discussed. It may be concluded that the damping mechanisms associated with 6063Al/Al2O3·SiO2
reinforced composites include mainly intrinsic damping, dislocation damping and interface damping.
However, only the interface damping mechanism is dominant at high temperature.

Abstract: Dissimilar friction spot lap joining of Al5052 and Al6022 sheet has been investigated
using a combination of joining parameters, thickness and upper plate material. The joining
parameters such as tool rotating speed, plunging depth and joining time have been considered. The
maximum tensile shear strength has been observed at tool rotating speed of 1000rpm, dwell time of
2.5sec, plunging depth of 1.8 mm and Al 6022 as upper plate. The maximum tensile shear fractured
load of the joint was about 80% of that of the similar Al 5052 alloys joint.

Abstract: The temperature evolution in inertia friction welded Inconel 718 joint was measured by means of embedding thermocouples in specimens. The spatial distributions of temperature in the axial and radial directions of weldments were obtained and the varying characteristics of the temperature distributions were analyzed. The results indicate that the heating rate during the inertia welding process decreases gradually. The temperature distribution in the radial direction of weldment is uneven and the temperature rises gradually with the increase of distance from the center. But the relation between the temperature and distance is nonlinear. In the axial direction, the shorter the distance from the initial friction surface is, the bigger the rate of temperature increment becomes and the higher the peak temperature and the temperature gradient are. Meanwhile, the longer the distance from the initial friction surface is, the later the peak temperature appears and the longer the delay time gets. Moreover, the results of microhardness testing in a welded joint prove that the measurement of temperature in this study is reliable.

Abstract: The effect of friction on compression load, effective strain, damage value and maximum principal stress were analyzed by rigid-plastic finite element method during multi-axial compressions (MAC). The results show that with the number of compressions, the maximum compression load increases gradually, the effective strain distributes ringwise and the maximum effective strain is in the center and the minimum at the surface. The damage is inclined to appear at the barreled shape perpendicular to the longitudinal axis. With the increase of friction coefficient, the maximum compression load, strain inhomogeneity, damage value and maximum principal stress increase under the condition of same number of compression. These results indicate that the friction is adverse during MAC. Appropriate measures should be adopted to decrease the effect of frictional force.

Abstract: A new method for determination of friction coefficient in sheet metal forming of Mg alloy AZ31B is presented in this paper. The method is based on the bulging test of sheet metal in which the specimen is processed with a hole at the center. The diameter of the hole will increase along the stroke of the punch and the dimensional change of the hole has a certain relationship with the friction coefficient at the punch/specimen interface. Thus, the friction coefficient can be determined indirectly according to the dimension of the hole in the bulging process. The bulging process of the sheet is simulated using FE code DEFORM-2D. The analysis model is set up according to the experiment of the bulging and the friction calibration curves are generated from the simulations of the bulging by setting different coefficients of friction. The friction coefficient can be determined by measuring the hole dimension during the bulging process and comparing it with the friction calibration curves.